Fertilisers containing potassium
must be applied wherever soil potassium reserves are inadequate for targeted
crop or pasture production.Potassium can be applied as
a straight fertiliser, or as part of a blended or compound fertiliser
with nitrogen and phosphorous.

Each of the major potash sources
are soluble in water and will readily dissolve when there is adequate
rainfall or irrigation is applied.Under high rainfall or excessive
irrigation, potassium can be lost in surface runoff or from the root zone
by leaching - especially in permeable soils with a low cation exchange
capacity.

Potassium is not lost to the
atmosphere, as can occur with some nitrogen fertilisers under certain
soil and environmental conditions.

Potassium can become unavailable
if it is fixed by expanding clay minerals, but will be slowly re-released
if soil exchangeable potassium levels fall.

Muriate
of Potash (MOP)

Potassium chloride (commonly
referred to as Muriate of Potash or MOP) is the most common potassium
source used in agriculture, accounting for about 95% of all potash fertilisers
used worldwide.

Its nutrient composition is
approximately:

Potassium: 50%
Chloride: 46%

MOP has a high nutrient concentration
and is therefore relatively price competitive with other forms of potassium.The chloride content of MOP
can also be beneficial where soil chloride is low. Recent research has
shown that chloride improves yield by increasing disease resistance in
crops.In circumstances where soil
or irrigation water chloride levels are very high, the addition of extra
chloride with MOP can cause toxicity. However, this is unlikely to be
a problem, except in very dry environments, since chloride is readily
removed from the soil by leaching.

Sulfate
of Potash (SOP)

Potash fertilisers other than
MOP are used where special crop or soil needs exist.

Potassium sulfate
(referred to as Sulfate of Potash or SOP) is used in crops that are sensitive to chloride
or fertiliser burn like tobacco, pineapple or avocado, or where sulfur
is deficient.

Its nutrient composition is
approximately:

Potassium: 41%

Sulfur: 18%

Potassium
Magnesium Sulfate

Potassium magnesium sulfate
is an excellent source of three of the major nutrients - potassium, magnesium
and sulfur.

Its nutrient composition is
approximately:

Potassium: 18%
Magnesium: 11% o
Sulfur: 22%

It is used mainly for high
value crops, where all three of these nutrients are required. It is also
included in many 'complete' fertiliser products since it supplies several
nutrients. While it is 99.7% water soluble, the rate of solubility is
too slow for application in fertigation systems.

Potassium
Nitrate

Potassium nitrate, sometimes
also known as saltpetre, is often used in foliar sprays or fertigation
because it is highly and quickly water soluble.

Its nutrient composition
is approximately:

Potassium: 38%
Nitrogen: 13%

Potassium nitrate has application
as a potassium source for crops which are highly sensitive to chloride,
such as tobacco.It
is an oxidising
agent and should be handled and stored with care.